Chemistry Reference
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precursor also resulted in Fe
2
P rods; long reaction times resulted in spherical
FeP with some hollow particles observed, attributed to the Kirkendall e
ect.
86
The inclusion of a palladium nanoparticle catalyst in the reaction of TOP
with preformed iron particles resulted in the synthesis of rods with
controllable dimensions, depending on palladium particle size and Fe : Pd
ratio.
87
The palladium particles acted as both a decomposition catalyst for
the iron particles, and as a catalytic centre for rod growth. The resulting rods
contained palladium throughout the length of the structure, indicating that
the palladium particles dissolved and reacted with the structure, possibly
forming a FePd alloy. Importantly, a closed synthetic system was required for
particle formation, and the constant
d
n
1
y
4
n
g
|
2
ow of an inert atmosphere was to be
avoided. This suggested the phosphorus precursor was PH
3
, generated by the
elimination of octene. In related work, CoP nanowires were prepared by the
thermolysis of Co(C
5
H
7
O
2
)
2
, with technical-grade TOPO, HDA and tetrade-
cylphosphonic acid (TDPA). In this case, the 90% pure TOPO was suggested
to be the phosphorus source.
88
TOP has also been used as a precursor in the preparation of FeP nanorods
and wires using Fe(CO)
5
, because anisotropic particles are of interest due to
the potential e
ect of shape on the magnetic properties of these materials.
The precursor was dissolved in TOP forming a TOP
iron carbonyl complex,
and injected into TOPO at temperatures above 300
C. Initially, rods were
found to form, which could be grown to micrometre-length wires by multiple
injections of precursors.
89
The use of multiple injections was extended to the
use of a syringe pump, to ensure a continuous introduction of precursors
into the reaction vessel,
90
allowing extra control over wire morphology. The
use of a syringe pump was then extended to the preparation of MnP, CoP and
Ni
2
P nanorods.
91
Nanowires of FeP have also been prepared using a related carbonyl
complex (
h
-
.
4
-C
6
H
8
)Fe(CO)
3
, which was thermolysed in TOPO, followed by the
addition of more precursor dissolved in TOP at 360
C.
92
The TOP was sug-
gested to coordinate to the particle surface, and at high temperatures
decomposed yielding phosphorus which di
used into the structure and
reacted, forming the FeP wire. Nanorods of Fe
2
P, 30
-
260 nm in length, have
also been prepared using similar chemistry, with multiple injections of
Fe(CO)
5
and TOP into a solution of 5 nm Fe
3
O
4
seeds, TOP and didode-
ceyldimethylammonium bromide at 300
C. The resulting rods with a Fe
3
O
4
/
Fe
2
P core/shell morphology exhibited unusual magnetic properties, notably
a variable blocking temperature dictated by the rod length, with a maximum
at 60 nm.
93
The synthesis of anisotropic MnP particles using Mn
carbonyl complexes
and TOP as precursors in a syringe pump stressed the importance of the
pump in producing particles with a rod morphology. Gregg
et al.
explored
this further by preparing anisotropic MnP particles by a simple injection
method, negating the need for a syringe pump.
94
In this method, a 50 : 50
(weight) mix of TOPO and TOP was heated at 350
C for 2 hours prior to
injection, to generate the phosphorus precursor. Mn
2
(CO)
10
was dissolved in
-
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